This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Human Keratinocytes were transfected with a cameleon calcium sensor and permeabilized with ionomycin. In the presence of calcium, FRET occurs between the cameleon CFP (donor) and YFP (acceptor) unit. In order to quantify the cameleon response to different calcium concentration, FLIM measurements of the donor fluorescence were performed and the data were analized using the phasor plot technique.